Answer: The property which is illustrated by the given equation, is associative property of addition.
Step-by-step explanation:
The associative property of addition states that the sum of three real number remains the same either start addition from first two numbers or last two numbers.
... (1)
The given equation is,

The above equation is same as equation (1)0, where the value of a, b and c are 2, x and 3 respectively.
And after simplifying the given equation we get,

The left hand side is equal to right hand side. So, the associative property of addition is illustrated by the given equation.